ndnhc's advices.
1. Use an escrow.
Details:
Get an escrow, transfer funds to be held with him as long as it is running. Funds should be a reasonable amount.
2. Lower the fee. A 5% is good enough. The lower the better
3. Make the game provably fair.
Details: You can hash the url of the winning satoshibox link or the number or both with random characters to avoid players brute-forcing it, using a one-way hashing function like SHA256, publish the hash before the game. When the winner is announced you will have to publish the message you hashed.
Illustration:
Your winning box is 102
http://satoshibox.com/55eae63WRFQWFe12fb6b456cYou hash 102:http://satoshibox.com/55eae63WRFQWFe12fb6b456c:randomtextndnhc using SHA256.
You get
e2ce2bf3a310658c603b92202e2819d2a319cc674bcd97d14b95c54bf530ba0f which you publish before the game, and the initial message after the game is over and the winner is declared.
Thanks
That would be 0.025
BTC.
Not intended to be taken seriously.